In 2012 the average Big Six SVT was £1030.78 a year, £72.57 more expensive than the cheapest available deal which cost £958.21 a year.

And in 2016 the average Big Six SVT was £1065.97, £168.79 more expensive than the best deal at £897.18 a year.

According to the latest Ofgem figures 45 per cent of households have never switched energy providers.

British Gas has the highest number of customers on its SVT at 6.6 million, with 3.1 E.On customers on an SVT. In total 18 million households are on SVT rates.

Bulb Co-founder Hayden Wood said: "These latest numbers show that so-called standard tariffs no longer have the customers’ best interests at heart. The Big Six need to show that they’re putting customers first, instead of profits.

"Loyalty towards a brand is often rewarded, yet households who’ve put their trust for years in a single energy company are being forced to subsidise others who switch every 12 months."